Male Scarlet Skimmers (sometimes called Oriental Scarlet) have a body length ranging from 40 to 43 mm.
The male is red from head to tail, including the eyes.
There is a distinctive thin dark line along the dorsum of the abdomen.
The female is light brown in colour and is easily distinguished by her entirely yellow legs and a white stripe running down over her body (clearly visible on the photo).
They can be easily confused with the Coastal Glider (Macrodiplax cora) which is widespread in Asia and Australia, but that species has a distinctive thick, broken dark line on the dorsum and the eyes are dark brown on the top half and black on the bottom half.
The Scarlet Skimmer is native to East and Southeast Asia, but it has been accidentally introduced into Hawaii and Florida in the USA, and spread to Cuba from Florida.

A female. Ubud, Bali, Indonesia, 16 October 2011